The present invention is related to apparatus for making up and breaking out rod joints of, for example, a drill string.
It is highly desirable to be able to break the threaded joints in a drill rod string by reversing the direction of a hydraulic motor. Generally the torque required to break the threaded joint exceeds the torque available from the hydraulic motor, even at the maximum hydraulic pressures. This is due to the joints tightening up during drilling which in turn is caused by torque peaks experienced during normal rotation of the drill rod string in a direction for increasing the depth of the bore hole.
In the prior art, for example see U.S. Pat. No. 4,266,444 to Anderson et al, it is old to provide rotary drive apparatus that includes a hydraulic motor for driving a first ring gear that in turn drives a second ring gear that is connectable to the member to be rotated and a third ring gear that is rotated by rack mechanism and is connectable through ratchet mechanism to drive the second gear when high torque is required to drive the second gear. The rack mechanism includes a piston cylinder combination for reciprocating the rack mechanism.
In U.S. Pat. No. 3,972,242 to Hunt there is disclosed a hydraulic wrench having a lock down cam that is fixedly connected to the piston rod of a cylinder to be reciprocated therewith and a rack that is connected to the piston rod through a lost-motion type connection such that when the piston rod is extended the cam first slides along the rack to force the rack teeth into intermeshing relationship with the teeth of the ratchet and thereafter move the rack to rotate the ratchet for tightening and loosening bolts and nuts. Thence, upon retracting the piston rod, first the cam is retracted sufficiently such that the rack can move out of intermeshing relationship with the ratchet and thereafter the rack is retracted with continued retraction of the cam.
In U.S. Pat. No. 2,019,814 to Holmes et al there is disclosed a chuck having a gear toothed ring intermeshing with a rack that is reciprocated by a piston cylinder combination.
In order to provide a simplified unit for making up rod joints and breaking out rod joints, including an initial slower speed higher torque force if necessary for breaking out the rod joint, this invention has been made.